Polydispersed composite emulsions

ABSTRACT

Multi-faceted technology for the combustion and transportation of emulsified hydrocarbon fuel. The fuel comprises a composite of a plurality of hydrocarbon in water emulsions. The composite emulsion has a unimodal hydrocarbon particle distribution, with the hydrocarbon being present in an amount of between 64% and 90% by volume.

TECHNICAL FIELD

The present invention relates to a emulsions formed from precursor emulsions having any particle modal distributions with the result being a unimodal emulsion with maximized desired chemical and physical characteristics.

BACKGROUND ART

Simple two phase emulsions are generally classified by the concentration of the dispersed phase, the size distribution of the dispersed droplets, and the rheological properties of the emulsion. Emulsions with 0-30% by volume of dispersed phase are known as low internal phase ratio emulsions (LIPR), 30-70% by volume of dispersed phase are known as medium internal phase emulsions (MIPR) and 70-100% by volume of dispersed phase are known as high internal phase emulsions (HIPR). The rheological behavior of an emulsion can be Newtonian or non-Newtonian. The extent of this behavior would depend upon the properties and concentrations of the two liquids used to make the emulsion. For emulsions consisting of oil-in-water (O/W), LIPR emulsions generally show Newtonian behavior. As the dispersed oil phase concentration increases, behavior becomes progressively more non-Newtonian.

R. Pal et al. [Emulsions in the Petroleum Industry Journal, Chapter 4, Rheology of emulsions] has shown that O/W emulsions can be considered Newtonian up to a dispersed phase volume of 0.4 (i.e. 40% dispersed phase). This was achieved by manufacturing O/W emulsions at different dispersed phase concentrations and measuring the shear stress (τ) at different shear rates (γ). All the emulsions contained droplets of the same mean diameter and were performed at a constant temperature.

The viscosity of an emulsion (η) is defined as the ratio of shear stress (τ) to shear rate ({dot over (γ)}). This is given by the equation:

τ=η{dot over (γ)}

The viscosity of a particular emulsion is dependent upon several factors, according to R. Pal et al. [Emulsions in the Petroleum Industry Journal, Chapter 4, Rheology of emulsions], being:

1. The viscosity of the continuous phase.

2. The volume fraction of the dispersed phase.

3. The viscosity of the dispersed phase.

4. The average particle size and distribution.

5. Shear rate.

6. The nature and concentration of the emulsifying agent.

7. Temperature.

The viscosity of the dispersed phase can sometimes play a part in determining the emulsion viscosity. This is especially true when internal circulation of the droplets occurs, which reduces the distortion of the flow field, resulting in a reduced viscosity of the emulsion. In such a system, an increase in the viscosity of the dispersed phase will result in decreased internal circulation and consequently increases the effective emulsion viscosity. When an emulsifying agent is present, internal circulation is greatly inhibited, and the dispersed phase droplets behave more like solid particles according to R. Pal et al. [Emulsions in the Petroleum Industry Journal, Chapter 4, Rheology of emulsions]. It is for this reason that some experiments discussed within this review involve solid particles in suspension rather than fluid droplets, as such a system behaves in a very similar manner.

Although all the above factors play their part in determining the emulsion viscosity, the most important is the volume fraction of the dispersed phase. It was Einstein who first showed that as the volume fraction of the dispersed particles increases, the viscosity of the system also increases. He proposed that the relative viscosity of a suspension is:

η_(r)=1+2.5φ

where η_(r) is the relative viscosity of the emulsion and φ is the volume fraction of dispersed phase. This equation is accurate but highly limited in its applicability. The suspension must be extremely dilute (less than 1% total volume of solids) so the particles are so far apart that there are no hydrodynamic forces acting (such as caused by van der Waals attraction and Brownian motion) and that the particles are rigid spheres. In such a system particle size would not affect the viscosity as long as the total volume remained under 1%.

Several empirical-based equations have since been proposed for predicting the relationship between viscosity and dispersed phase concentration. The most popular and widely used equation is the Krieger-Dougherty equation:

$\eta_{r} = \left\lbrack {1 - \frac{\varphi}{\varphi_{\max}}} \right\rbrack^{{- {\lbrack\eta\rbrack}}\varphi_{\max}}$

where φ_(max) is the maximum packing concentration of the dispersed phase and [η] is the intrinsic viscosity which is a measure of the ability of the particles to influence the viscosity (=2.5 for rigid spheres).

Another popular equation used to predict dispersion viscosity is the Mooney equation,

$\eta_{r} = {\exp\left\lbrack \frac{2.5\; \varphi}{1 - {K\; \varphi}} \right\rbrack}$

where K is a constant reflecting droplet packing.

A commonly used model to represent packing of droplets in a mono-disperse emulsion assumes that all are non-deformable spherical droplets. It has been calculated that the maximum packing fraction (φ_(max)) of such a system is 0.74. This maximum is achieved when the uniform spherical droplets are packed hexagonally within the continuous phase. This model for maximum packing concentration applies when assuming the dispersed phase consists of non-deformable spherical objects, but in the reality of emulsion systems, it is possible for the packing concentration to exceed the maximum packing concentration but the dispersed droplets would not remain spherical. If this is the case then the above model would not be accurate according to R. Pal [Colloids and Surfaces A: Physiochem. Eng. Aspects, 137 (1998) 275-286, A novel method to correlate emulsion viscosity data].

The Krieger-Dougherty equation appears to adequately fit most collected data for emulsions with a total volume fraction up to the critical deformation volume fraction (φ_(d)). This is the point at which high levels of droplet deformation can occur under shear stress. The critical deformation volume fraction is variable for different emulsions and depends on both the properties of the dispersed phase and the emulsifying agent used. As the total volume fraction increases, emulsion rheology becomes less Newtonian. Viscosity predicting equations such as the Krieger-Dougherty equation and the Mooney equation are not exact, but are based upon experimental data and various assumptions. They show accuracy at lower volume fractions but their limitations are shown at higher volume fractions where deviations also occur in experimental data.

Unique rheological properties have been noticed in various bimodal systems over recent years. These effects, to be discussed, have been observed in emulsions (ranging from LIPR to HIPR) and also in suspensions (dilute through to concentrated) and with or without colloidal forces present.

The following properties have been observed in composite emulsions and suspensions:

-   -   Increased maximum packing fraction;     -   Reduced viscosity;     -   Reduced shear-thinning effect (generally emulsions) at a given         packing fraction;     -   Reduced shear-thickening effect (generally suspensions) at a         given packing fraction;     -   Reduced storage/loss moduli.

It was observed by Chong et al. [Journal of Applied Polymer Science, 15 (8) 2007; 1971, Rheology of concentrated suspensions], in 1971 that by mixing two separate suspensions, each consisting of different sized particles, the rheological properties of the combined suspension were significantly altered at certain volume fraction mixtures. Their experiment measured the relative viscosity of mono-disperse and bi-disperse suspensions, and, at certain volume percent combinations, the bi-disperse suspension exhibited a significantly lower viscosity than the two component mono-disperse suspensions. This was apparent to different extents at solid packing concentrations between 0.55 and 0.65.

The minimum viscosity appeared to occur in each case at approximately 40% small spheres in the total solids. It was also noticed that by increasing the size difference between the small and large spheres, it was possible to reduce the viscosity further at this point according to Chong et al. [Journal of Applied Polymer Science, 15 (8) 2007; 1971, Rheology of concentrated suspensions].

In order to maximize the viscosity reduction in a bimodal system, there are three main variables that can be observed even in this very early research:

-   -   Total volume fraction of the dispersed phase;     -   Proportion of fine droplets/particles;     -   Diameter ratio of the fine and coarse droplets/particles.

There are different theories proposed as to why this decrease in viscosity occurs when fine particles or droplets are added to larger ones. One popular way of looking at the situation is in terms of the maximum packing fraction. It can be seen from the Krieger-Dougherty equation that the maximum packing fraction directly governs the viscosity of the suspension or emulsion. If fine particles are added to a lattice of larger particles, they are able to position themselves in spaces in between the larger particles, the result being that there is a greater total available space and hence an increased maximum packing fraction. The increased space available would mean a greater fluidity within the system and therefore a lower viscosity.

Greenwood et al. [Colloids and Surfaces A: Physiochem. Eng. Aspects, 144 (1998) 139-147, Minimising the viscosity of concentrated dispersions by using bimodal particle size distributions] designed a detailed experiment to observe the effect of the composition (of small particles compared to large particles) on the rheological properties of a bimodal suspension. The diameter ratio of small to large particles used in their experiment was 4.76. They report this as the ratio where they have observed a minimum in viscosity. Their work involved measuring the viscosity of various bimodal suspensions containing between 10% and 35% small particles by volume. Viscosity measurements were taken for these different suspensions at total volume fractions between 0.45 and 0.65.

These results indicate that a minimum viscosity occurs at a composition of 0.2 small particles by volume for each of the different total volume fractions. It can also clearly be seen that this drop in viscosity becomes significantly more pronounced as the total volume fraction increases.

An alternative way to view the situation is in terms of flocculation/aggregation within the system. There are various instability mechanisms that can act in an emulsion to different extents, namely coagulation/coalescence, creaming/sedimentation, Ostwald ripening and flocculation/aggregation. Increased flocculation in an emulsion resulting from increased droplet-droplet interactions has the effect of increasing its viscosity. However, by replacing some of the coarse droplets with fine droplets, it is considered to have the effect of breaking up the flocculation interactions between the larger droplets. This results in greater mobility of the droplets within the emulsion and a subsequent reduction in viscosity. As the dispersed phase volume fraction increases, flocculation becomes stronger (as the dispersed phase droplets are closer together), and so the addition of finer droplets causes a more significant reduction in viscosity as explained by R. Pal [Chemical Eng Journal, 67 (1997) 37-44, Viscosity and storage/loss moduli for mixtures of fine and course emulsions].

The two theories mentioned within this section both describe mechanisms by which the reduction in viscosity is achieved. The reality of the situation is likely to be a combination of the two, both contributing to different extents.

As mentioned previously, when modeling a mono-disperse suspension of non-deformable spherical droplets, the optimum packing structure (hexagonal lattice formation) would result in a maximum packing concentration of 0.74. In bidisperse suspensions, however, the maximum packing concentration, and consequently the viscosity, will depend upon the relative contribution (by volume) of the different sized particles being mixed together. It would also depend on the shape of the particles and their size distribution.

The maximum packing concentration can also be reduced if aggregation occurs within the system as this can trap fluid between solid particles.

It was proposed by Farris in 1968 [Trans. Soc. Rheol.—12.281] that in a bimodal suspension where there is a significant size difference between the small and the large particles, the small particle suspension acts as the suspending medium for the large particles. Such a system suggests that the small particles could pack tightly in between the larger particles, resulting in the possibility of a much greater maximum packing concentration. Farris proposed figures for optimum compositions of small and large particles at various packing concentrations between 70% and 86% tabulated in Table 1.

TABLE 1 Optimum composition of small and large particles to achieve specific concentrations (from Farris [Trans. Soc. Rheol. - 12.281(1968)]. Total volume (%) Small (%) Large (%) 70 35.5 64.5 72 34.5 65.5 74 33.5 66.5 76 33.0 67.0 78 32.0 68.0 80 31.0 69.0 82 30.0 70.0 84 28.5 71.5 86 27.5 72.5

It can be seen from the data in Table 1 that as the packing concentration increases so the optimum proportion of small particles decreases. The results obtained by Chong et al. [Journal of Applied Polymer Science, 15 (8) 2007; 1971, Rheology of concentrated suspensions] showed a minimum viscosity occurring at approximately 40% at packing concentrations between 0.55 and 0.65. These observations appear to be in agreement with the data quoted above.

This system results in greatly improved packing efficiency and a consequent increase in system fluidity according to Tsenoglou and Yang [Polymer Engineering and Science, Mid-November 1990, Vol 30, No 21, Fluidity and optimum packing in suspensions of mixed dissimilar particles]. The industrial relevance of this could be to create a bimodal suspension (or emulsion) containing an increased dispersed volume fraction with the same viscosity as a mono-modal system. Alternatively, the technology could be used to create a bimodal system with the same dispersed volume fraction but with a significantly reduced viscosity compared to a mono-modal system.

It was also observed that in a bimodal suspension, the volume fraction of particulate at which shear thickening increased was raised [Wagstaff & Chaffey, Journal—J Colloid Interface Sci, 59 (1977) 53]. R. Pal [Chemical Eng Journal, 67 (1997) 37-44, Viscosity and storage/loss of moduli for mixtures of fine and course emulsions] has also reported that there is a reduction in the shear thinning effect of course emulsion when a fine emulsion is added, indicating the significance of bimodal systems in controlling rheological properties other than viscosity.

The vast majority of testing relating to bimodal suspensions has been based around systems where the particles are large enough so that there are only negligible colloidal forces acting. This could be due to researchers trying to simplify the system or because the greater proportion of industrial uses would involve larger particles. However, D'Haene and Mewis [Rheological Acta, Vol 33, No 3 (1994), Rheological characterization of bimodal colloidal dispersions] have investigated the rheological effect of particle size distribution on a colloidal suspension where many more forces are involved. They used particles of diameter 129 nm and 823 nm (i.e. a diameter ratio of 6.38). It was shown that the viscosity goes through a minimum in the same way as a suspension with negligible colloidal forces present. As is the case with other investigations, this minimum is also achieved at 25% small particles by volume. It was also observed that if the composition of small particles exceeds 50% then the viscosity becomes almost independent of the composition.

The minimum viscosity achieved was measured to be almost 200 times smaller than that of the pure fine fraction. One point to note with regard to this particular system is that the layer of dispersant that surrounds the particles becomes much more significant when the particles are small. In this case, the minimum viscosity is occurring at 25% small particles by volume, but the effective volume fraction calculates as 31.6% when the dispersant layer is taken into account.

Solid spheres can pack in many different ways, but generally it is a mixture of simple cubic (φ_(max)=0.524) face-centered cubic (φ_(max)=0.740) and hexagonal close packing (φ_(max)=0.740). The mixture known as random close packing has a maximum packing fraction of 0.639 (average obtained from several publications). This is only a simplified model, but it appears to relate well to experimental findings. When considering emulsions, however, various other factors such as droplet deformability and various instability mechanisms (such as flocculation and coalescence) also become important.

When considering the closest possible packing of solid spheres, and consequently the smallest possible pore size that could occur, as shown in FIG. 2 for example, it is possible to calculate the pore diameter (D_(p)) in relation to sphere diameter (D_(s)) using relatively simple geometry. In this situation, the following formula is obtained to relate pore and sphere diameters:

$D_{p} = {{D_{s}\left( {\frac{2}{\sqrt{3}} - 1} \right)} = {0.154\; D_{s}}}$

As a result the critical diameter ratio for a small sphere that would fit exactly into the pores created by larger spheres would be 6.49.

In 1997, Greenwood et al. [J. Colloid Interface Sci, 191, 11-21 (1997), The effect diameter ratio and volume ratio on the viscosity of bimodal suspensions of polymer lattices] focused attention on determining both the optimum diameter ratio and the optimum proportion of small particles in a bimodal suspension. Mono-disperse suspensions were prepared of the fine and coarse particles, and bidisperse suspensions of 25%, 50% and 75% small particles by volume. Viscosities of these suspensions were measured at particle diameter ratios of 1.08, 2.81, 4.03, 5.67, 6.37, 7.83 and 11.15.

After initially showing that (in agreement with most research to date) a minimum relative viscosity generally occurred at 25% small particles by volume, these workers found that the lowest viscosity was achieved with a diameter ratio of 7.83. The ratios of 4.03, 6.37 and 11.15 also exhibited a lower viscosity than that of the large particle mono-disperse suspension. FIG. 2 shows the viscosities at 25% small particles by volume [Greenwood et al. [J. Colloid Interface Sci, 191, 11-21 (1997), The effect diameter ratio and volume ratio on the viscosity of bimodal suspensions of polymer lattices]].

Focus was then shifted to each of the individual diameter ratios and the effect of small particle contribution on the viscosity was measured.

FIG. 3 shows the results at a diameter ratio of 6.37 where the viscosity minimum can be observed at 25% small particles as expected. Neither FIG. 4 (diameter ratio 2.81) nor FIG. 5 (diameter ratio 1.08) show a reduced viscosity at 25% small particles at any concentration, possibly because the small particles are not small enough to fit into the voids created by the larger particles.

A diameter ratio of 1.08, however, does exhibit a minimum in viscosity at 75% small particles that is lower than that of the large particles alone. Although it is only a minor reduction, it does occur at all concentrations tested. There do not seem to be any detailed explanations behind these results in the original paper, although due to it being observed at numerous concentrations it may be an area that requires some attention in the future.

Significantly less research has been carried out on bimodal emulsions than for suspensions, but Pal has conducted experiments for such a system [Chemical Eng Journal, 67 (1997) 37-44), Viscosity and storage/loss moduli for mixtures of fine and course emulsions]. Pal designed his experiment to observe the effects of a bimodal emulsion in HIPR systems, both O/W and W/O. He prepared fine (6.5 μm) and coarse (32 μm) O/W emulsions (size ratio of 4.92, very similar to that of Greenwood et al. [Colloids and surfaces A: Physiochem. Eng. Aspects, 144 (1998) 139-147, Minimising the viscosity of concentrated dispersions by using bimodal particle size distributions] and mixed them in different ratios to total oil volume fractions of 0.41, 0.63 and 0.78. The emulsions were prepared using a variable speed homogenizer, keeping the shearing speed small to prepare the coarse emulsion and increasing it to prepare the fine emulsion.

For the different proportions of the fine emulsion, viscosity was measured at each of the total oil volume fractions. The results obtained are shown in FIG. 9 [R. Pal [Chemical Eng Journal, 67 (1997) 37-44), Viscosity and storage/loss moduli for mixtures of fine and course emulsions]].

The results indicate that the minimum in viscosity occurs at 28% fine droplets by volume, and that at higher total oil volume fractions this reduction in viscosity is greater than at lower volume fractions. The results are consistent with previous experimental data of solid particles in a bidisperse suspension. Pal also noticed a minimum in the storage/loss moduli at the same composition of fine particles.

Intevep have undertaken a great amount of research into the application of bimodal emulsions in the process of viscous hydrocarbon removal (for examples: U.S. Pat. No. 5,503,772 entitled “Bimodal emulsion and its method of preparation”[2 Apr. 1996]; U.S. Pat. No. 5,419,852 entitled “Bimodal emulsion and its method of preparation [30 May 1995]”; U.S. Pat. No. 5,603,864 entitled “Method for the preparation of viscous hydrocarbon in aqueous buffer solution emulsions”[18 Feb. 1997]; U.S. Pat. No. 6,903,138 entitled “Manufacture of stable bimodal emulsions using dynamic mixing” [7 Jun. 2005]; U.S. Pat. No. 5,622,920 entitled “Emulsion of viscous hydrocarbon in aqueous buffer solution and method for preparing same”[22 Apr. 1997]; U.S. Pat. No. 5,556,574 entitled “Emulsion of viscous hydrocarbon in aqueous buffer solution and method for preparing same” [17 Sep. 1996] and U.S. Pat. No. 5,480,583 entitled “Emulsion of viscous hydrocarbon in aqueous buffer solution and method for preparing same” [2 Jan. 1996]. Previous use of emulsions has been limited to an extent by the volume of hydrocarbon that can be dispersed within the emulsion and the resultant viscosity obtained. It has been possible to increase the total volume up to 85% and achieve a resultant viscosity of 1500 cps at 30° C.

The long term stability of the emulsion have also been considered, with regard to dehydration and desalting as this is an important property considering transportation of the emulsion. It is claimed in these patents that the primary controlling factor of the viscosity is the proportion of small and large droplets.

An ethoxylated alkylphenol emulsifying agent was used at a concentration of 3000 mg/l of oil to produce the coarse emulsion and a concentration of 5000 mg/l of oil for the fine emulsion. Diameter ratios of 14, 7 and 6 were tested and all produced viscosities well below the two constituent emulsions. The lowest viscosities achieved were at diameter ratios greater than 10. This figure is greater than the previously calculated value of 6.49 for hard spherical objects, and could be due to high levels of droplet deformation occurring at 80% total volume. In their testing, the diameter of the coarse droplets was between 15 and 30 microns. The emulsions were prepared by dynamic mixing at 60° C., and the mixing speed and duration was altered to form the different droplet sizes.

The viscosity of dispersions is affected by several factors, with the volume fraction of the dispersed phase and the average particle size and distribution being of particular interest. The viscosity is known to increase as the volume fraction of the dispersed phase increases, and also as the average particle/droplet size decreases. This can be extremely limiting in industry when trying to disperse a high volume fraction of a highly viscous liquid or a solid, as it is necessary to reduce viscosity to manageable levels for purposes of transport and handling.

It has been observed that by mixing two separate dispersions with different mean particle sizes that it is possible to achieve a viscosity lower than that of either component dispersion. The composite dispersion also allows for a greatly increased maximum packing fraction, reduced shear-thinning or shear-thickening behavior and reduced storage/loss moduli.

Three main variables have shown to affect the viscosity reduction in a composite dispersion. The addition of fine particles to a dispersion of larger particles increases the volume fraction of the dispersed phase, by filling the voids created by the large particles they increase the maximum packing fraction, increase the fluidity and reduce viscosity. The mixing ratio of these fine and coarse particles is important, and maximum fluidity has been found to be achieved at 20-30% small particles by volume. It is also vital that the particle diameter ratio is correct to achieve improved fluidity in the dispersion. By studying the geometry of particle packing it has been found that, assuming all particles are solid spheres, the fine particle diameter must be 6.49 times smaller than the large particle diameter to be able to fit into any of the voids created by the lattice of large particles. Experimental evidence suggests that maximum viscosity reductions are likely to be achieved at diameter ratios greater than 6.49, as in reality it is very unlikely that all particles will be hard spherical objects. Emulsion droplets for example will, at high dispersed phase concentrations, be deformed and as a result the voids between droplets will be reduced in size from the model used and an increased diameter ratio will be required for fine droplets to fill these voids.

Knowledge of composite dispersions is already being applied in various industries to great advantage. Achieving advantageous rheological properties with bimodal dispersions of polymers such as latex has become important in the preparation of many products such as paints, adhesives, rubbers, inks, coatings, sealants and many more. Low viscosities are achieved by dispersing two or more mean polymer lengths in accordance with the fundamentals previously mentioned. The coal industry has spent time developing systems to suspend coal particles of different sizes in water to form slurries that can be easily transported and combusted directly as an alternative energy source to oil. The recovery of viscous hydrocarbons has been aided by dispersing them as a bimodal oil-in-water emulsion with a greatly reduced viscosity to aid transport and improved storage stability.

Other applications include cosmetics such as sunscreen where a bimodal dispersion improves the sunscreen protection factor due to increased film-forming properties. The knowledge is used in many aspects of the food industry and has potential applications in many areas of medicine such as in drug delivery systems.

As a first emulsion, emulsified hydrocarbon fuels have become increasingly important as a useful fuel for steam generation in power plant and other steam raising facilities to replace coal and petroleum coke, has environmental drawbacks, and natural gas which is relatively more expensive. The high cost of natural gas has particular ramifications in the petroleum processing art and specifically in the steam assisted gravity drainage technique (SAGD) as related to the production of heavy oils and natural bitumens. As is known, the SAGD and congener techniques require the use of steam generators for injecting steam into a subterranean formation to mobilize highly viscous hydrocarbon material. Conventionally, natural gas has been used to fire the steam generators, however, this is unattractive from a financial point of view and has other inherent drawbacks. With the advent of emulsified hydrocarbons, especially those manufactured from hydrocarbons or their products from indigenous hydrocarbon production, it has been found that the heat content is adequate to burn in a steam generation environment.

One of the first pioneering fuels in this field was Orimulsion, manufactured in Venezuela by Bitor, and shipped worldwide to supply power generation plants. Building on the success of Orimulsion, other emulsified fuels have been developed such as MSAR™ (Multi-Phase Superfine Atomized Residue), by Quadrise Ltd. and now further developed by Quadrise Canada Fuel Systems, Inc. MSAR™ is an oil-in-water emulsion fuel where the oil is a hydrocarbon with an API gravity between 15 and −10. Typical oil-water ratios lie in the range 65% to 74%. Because of the presence of oil droplets in water, MSAR™ is essentially a pre-atomized fuel. This means that the burner atomizer does not do mechanical work to produce oil droplets, as in conventional fuel oil combustion, but that it is the emulsion manufacturing equipment that produces the oil droplets. Pre-atomization literally means ‘before the atomizer’ and so the MSAR™ manufacturing equipment is essentially the atomizer of this process. Typical mean droplet size characteristics of MSAR™ are around 5 microns, whereas typical mean droplet size characteristics produced during fuel oil atomization in a burner atomizer are between 150 and 200 microns. Therefore, the enormous increase in surface area brought about by producing much smaller droplets in the MSAR™ production process, compared with a conventional burner atomizer, leads to much more rapid and complete combustion, despite the fact that there are significant quantities of water present. In addition, when MSAR™ passes through a conventional atomizer, as it must do in order to be combusted, 150-200 micron water droplets containing the 5 micron oil droplets are formed. Water therefore finds itself located in the interstitial zones between each assembly of oil droplets. This interstitial water, between the oil droplets, spontaneously vaporizes and this leads to further break-up of the already small (5 micron) droplets. This process is known as secondary atomization. Because of this secondary atomization and the earlier described pre-atomization, MSAR™ has been found to be a particularly effective fuel, with a carbon burnout rate of 99.9%. Carbon burnout is obviously an important aspect of any combustion process and the fact that MSAR™ carbon burnout is so high, substantially reduces the amount of carbon coated ash that collects in the burner and/or furnace. As is known, if the carbon burnout is low, then carbon will deposit with ash and on boiler surfaces and will effectively lead to the production of coke; this leads to inefficiencies and/or inoperability in the overall process. By providing a 99.9% carbon burnout rate, these problems are obviated.

Whilst the extremely small droplet size associated with MSAR™ has distinct advantages for the combustion process, it has disadvantages for the handling and pumping processes because the smaller the droplets, the more viscous the MSAR™. Therefore, in order to further advance emulsion fuel technology, present research, conducted by other organizations, has developed means by which the extremely small droplet size can be maintained whilst simultaneously reducing viscosity leading to improvements in storage, handling and transportation generally. Consequently, research has gone in the direction of bimodal emulsions, i.e. emulsions which have two distinct droplet size peaks in their droplet size profile.

Exemplary of this is U.S. Pat. Nos. 5,419,852 issued May 30, 1995 to Rivas, et al and 5,503,772, issued Apr. 2, 1996 to Rivas et al, inter alia. In these references, specific blends of independently produced and discretely different characteristic emulsions are used to describe the invention. The conclusion is made that the bimodal emulsions can be prepared to reduce viscosity and illustrate that the final emulsion is distinctively bimodal in its physical characteristics.

Although it is desirable to have a bimodal emulsion, this technology is not without limitation. It is known in the art that the larger the average particle size is, the lower the viscosity of the mixture. Unfortunately, the larger the particles in an emulsified fuel, the greater the length of time it takes for the oil droplet to combust and travel down the furnace which results in the requirement for a longer furnace. This also limits the quantity of water that can be interstitially incorporated. The benefits of this have been discussed herein previously in the analysis of the prior art and relevant literature. In terms of the furnace, if it is of an insufficient length for the selected fuel, then unburnt hydrocarbon material and/or smoke become undesirable attributes. In this manner, the existing technology is limited by the equipment used which can add costs, complications and other problems related to pollution in the overall process.

Given the state of the art, it has now been recognized that the viscosity drives the overall system towards bigger oil droplets in the fuel, while the combustion results in the driving of the system towards smaller oil droplets. Accordingly, it would be desirable to have a formulation that results in the change in the particle size distribution of the fuel emulsion to reduce viscosity, but also to improve combustion. These latter two properties are most desirable to provide a very efficient high enthalpy emulsified fuel. Having the formation of an emulsion with the above noted properties as a goal, a novel approach was taken to resolve these properties into an emulsion.

It was found particularly effective to look at the packing of particles in the prior art and adopt this technology. This had not previously been applied to the field of emulsions for the purpose of generating a composite emulsion having the most desirable properties, namely a broad particle distribution composed of n-modal distributions, but maintaining, as far as is practically possible, the n-modal distributions as a single peak; i.e., a unimodal distribution

Representative of the particle packing references was gleaned from the Journal of Computational Physics 202 (2005), 737-764, and particularly an article entitled Neighbor list collision-driven molecular dynamics simulation for non-spherical hard particles. I. Algorithmic details. A general algorithm for a system of particles having relatively small aspect ratios with small variations in size. The article was authorized by Donev et al. A further article by the same author entitled, Neighbor list collision-driven molecular dynamics simulation for non-spherical hard particles. II. Applications to ellipses and ellipsoids, Journal of Computational Physics 202 (2005), 765-793, was also reviewed. Other general references in the spherical packing technology include: the article Modeling the packing of granular media by dissipative particle dynamics on an SGI Origin 2000, using DL _(—) POLY with MPI, Elliott et al; Packing and Viscosity of Concentrated Polydisperse Coal-Water Slurries, Veytsman et al, Energy and Fuels 1998, 12, 1031-1039; Is Random Close Packing of Spheres Well Defined? Physical Review Letters, 6 Mar. 2000, Torquato et al.; and The random packing of heterogeneous propellants, KNOTT et al.

In U.S. Pat. No. 4,725,287, Canadian Occidental Petroleum, Ltd., issued on Feb. 16, 1988, a general equation,

$\mu = {\mu_{o}\exp \frac{2.5\; \phi}{1 - \left( {\phi/\phi_{p}} \right)}}$

where

-   -   μ=oil-in-water emulsion viscosity (cs)     -   μ_(o)=viscosity of the water continuous phase (cs)     -   φ=volume fraction of the dispersed oil phase     -   φ_(p)=maximum packing fraction for the emulsion oil droplet size         distribution

is presented, which links the viscosity to the maximum packing of a specific particle size distribution.

The equation illustrates that the viscosity of an oil-in-water emulsion may be reduced if the oil droplet size distribution results in a larger maximum packing fraction. This reduction may be accomplished by forming the oil-in-water emulsion such that a wide range of oil droplet sizes results, or by the formation of a bimodal oil droplet size distribution. By way of example only, in comparison to a monodisperse oil-in-water emulsion with φ=0.5, a bimodal oil-in-water emulsion with an oil droplet size ratio of 5 to 1 theoretically has a viscosity reduced by a factor of about 10, assuming spherical and non-interacting oil particles. The larger this maximum packing factor, the lower the viscosity. As a general comment, it is noted that a single emulsion with a wide particle size distribution will have a lower viscosity. Further, it is known that bimodal emulsions have a lower viscosity and that not all mixtures of emulsions will lead to a reduction in viscosity. Although useful general teachings, the reference does not specify how to eliminate the “guesswork” from selecting which particle size results in maximum polydispersity in a unimodal emulsion.

In U.S. Pat. No. 5,283,001 (Canadian Occidental Petroleum, Ltd.), issued on Feb. 1, 1994, a general overview of mixing emulsions is given. It is indicated that:

-   -   . . . a bimodal or multimodal oil-in-aqueous phase emulsion(s)         may be formed with any of the emulsifying agent(s) of the         present invention by varying the residence times and/or the         shear rate of the mixture of emulsifying composition(s) and         produced hydrocarbon crude in any suitable dynamic shearer and         mixer (e.g. a rotor stator mixer, etc.), and collecting the         effluent oil-in-aqueous phase emulsion(s) emanating from the         dynamic shearer and mixer at various residence times and/or         shear rates in any suitable tank or container, such as emulsion         tank 122. The collected effluent oil-in-aqueous phase         emulsion(s) produced from various residence times and/or shear         rates in any suitable dynamic shearer and mixer combine in the         emulsion tank 122 to form bimodal or multimodal oil-in-aqueous         phase emulsion(s) having a lower viscosity of oil-in-aqueous         phase emulsion(s) produced from one dynamic shearer and mixer         having a fixed shear rate and/or residence time of the         emulsifying composition(s) and the produced hydrocarbon crude in         the dynamic shearer and mixer; or from the static shearing and         mixing device 108 with one flow (and shear) rate. Thus, by way         of example only, the viscosity of a bimodal oil-in-aqueous phase         emulsion(s) produced by positioning for 4 secs. a mixture of         emulsifying composition(s) and produced hydrocarbon crude in a         dynamic shearer and mixer having a shear field intensity of 500         sec.⁻¹, and combining the resulting oil-in-aqueous phase         emulsion(s) with the oil-in-aqueous phase emulsion(s) formulated         from subsequently positioning for 4 secs. the same mixture in         the same dynamic shearer and mixer having a shear field         intensity of 6,000 sec.⁻¹, would be lower than the respective         viscosities of the oil-in-aqueous phase emulsion(s) produced         with an intensity of 500 sec.⁻¹ or 6,000 sec.⁻¹. Similar results         can be obtained by varying the residence time while holding the         shear field intensity generally constant or fixed.

The fact that mixing emulsions (two or more) gives a reduction in viscosity is acknowledged. The final emulsion can be either multimodal or bimodal.

This art is useful to provide teachings revolving around bimodal or multimodal emulsions, but nothing concerning unimodal emulsions. The patent provides an example at column 88, line 48 et seq.:

Example XIX

-   -   The Example is presented to prove that bimodal oil-in-water         emulsion(s) has an improved viscosity. The crude was Manatokan.         The aqueous phase was water. The surfactant was a mixture of         714.3 ppm NP40 (714.3 ppm of NP40 by weight of Manatokan) and         714.3 ppm NP100 (714.3 ppm of NP100 by weight of Manatokan). The         emulsifying composition was prepared by mixing water with the         surfactant. Two oil-in-water emulsions were prepared by mixing a         known amount of the emulsifying composition(s) with a known         amount of the Manatokan and agitating with a rotor-stator mixer         having a mixer energy of 3000 rpm for 40 secs. The first         oil-in-water emulsion(s) had a mean oil droplet size (μ) of         69.9, a dispersity of 3.27, and a viscosity (cp) of 221. The         second emulsion with less Manatokan had a mean oil droplet size         of 54.9, a dispersity of about 3.56, and a viscosity (cp) of         about 198. When 1 liter of the first emulsion was mixed with 1         liter of the second emulsion a third oil-in-water emulsion was         produced having a mean oil droplet size of about 61.7, a         dispersity of about 3.88 and a viscosity (cp) of about 140.         Thus, bimodal emulsion have a lower viscosity than any of its         emulsion constituents.

An example is given where two emulsions are mixed in a 50/50 ratio. The results illustrate reduced viscosity of the final emulsion compared to the two precursor emulsions; however, taking a different ratio would have resulted in a much different viscosity that would have been higher than one of the two precursor emulsions”. Further, in column 110, beginning at line 29, it is indicated:

-   -   Emulsion Viscosity     -   All of the asphalt emulsions produced with 30-per-cent water         fall within a relatively narrow range of viscosity, typically         130-150 cp at 120° F. The variation with temperature was much         less sensitive than for oils or heavy crude emulsions, as shown         in FIG. 21. As with other WCE's, decreasing the water content         causes an increased viscosity, for example, the run BEPU-21         emulsion at 25% water had a viscosity of 309 cp.

The fact that emulsion viscosity increases with hydrocarbon content is shown as an example; however, no teachings are directed to a composite emulsion with reduced viscosity.

In view of the prior art in the emulsion field, there still exists a need for an emulsion which facilitates changes in particle size distribution of the fuel emulsion to reduce viscosity, but also one which has improved combustion and does not lead to poor carbon burnout. The technology herein provides for burn optimization of the emulsion.

By applying the packing models from solid fuel to the instant technology, it was found that the wider the particle size distribution, the lower the viscosity of the emulsion.

The present invention has now collated the most desirable properties for a fuel emulsion where the final emulsion is effectively a composite emulsion of at least two precursory emulsions and which composite emulsion provides for a unimodal distribution, i.e. a single peak, emulsion as opposed to bimodal distribution which is exemplified in the prior art. Unimodal as used herein, refers to a majority peak with the potential for shoulders, but absent discrete peaks. This may also be defined as having a unique volumetric mode where the volumetric probability of finding particles on each side of the mode is monotonically decreasing and there are no other local maxima.

The present invention has successfully unified unrelated technologies to result in a particularly efficient composite fuel emulsion and methodology for synthesizing fuels regardless of the characteristic of the precursor emulsions, while fully controlling polydispersity.

INDUSTRIAL APPLICABILITY

The present technology has industrial applicability in the emulsion synthesis field.

DISCLOSURE OF THE INVENTION

One aspect of the present invention is to provide a substantially improved atomized fuel emulsion, which emulsion is a composite fuel emulsion having very desirable burn properties, calorific value and which can be custom designed for burning in any furnace or burning arrangement which is vastly different from the prior art.

According to a further aspect of one embodiment of the present invention, there is provided an emulsified hydrocarbon fuel, comprising a composite of a plurality of hydrocarbon-in-water emulsions, the composite emulsion having a unimodal hydrocarbon particle distribution, the hydrocarbon being present in an amount of between 64% and 90% by volume.

As noted herein previously with respect to the prior art, high oil content in the oil-in-water emulsion has been recognized previously, however, the emulsions formed in the prior art are not unimodal; local maxima exist on either side of a mode. By making use of the instant technology, not only is the hydrocarbon content exceedingly high, but the viscosity is reduced for the overall system relative to the independent viscosities of the precursor emulsions forming the composite and further, the carbon burnout rate is particularly attractive at greater than four nine effectiveness.

Turning to U.S. Pat. No. 5,419,852 (Invetep, S. A.), issued on May 30, 1995, there is discussed a stable, low viscosity bimodal viscous hydrocarbon in water emulsion. The text indicates that the emulsion has low viscosity and superior aging properties. A method for synthesizing the emulsion is also taught. The invention is further drawn to a method for the preparation of such a bimodal viscous hydrocarbon in water emulsion. This patent concentrates on bimodal emulsions and specific mixing ratios of average particle size diameter and specific ratios of the two precursor emulsions.

Absent the disclosure are details concerning:

-   -   i) unimodal composite emulsions;     -   ii) use of different hydrocarbons for the precursor emulsions;     -   iii) the lack of a specific requirement for a specific average         particle size ratio;     -   iv) the lack of a specific requirement for a specific mixing         ratio; and     -   v) methodology for finding the best average particle size ratio         and the best mixing ratio using a predictive model.

A significant advancement with the present technology is the formulation of a way to formulate composite emulsions where the polydispersity can be controlled much better than if we were looking at a single precursor emulsion. There are too many ways to create polydispersed emulsions that would either not work or be very hard to control. The instant technology teaches a way to make a composite emulsion from whatever precursor emulsion is used. This is in marked contrast to the reference discussed above, where there is taught a way to make a composite emulsion from two very specific precursor emulsions.

Further, in U.S. patent application Ser. No. 10/162,042 (Gurfinkel Castillo, Mariano E. et al.), another variation on the emulsion formation technology is set forth. The text of the application indicates:

-   -   Second portion 62 is mixed with hydrocarbon 70 in a mixer of         module 54 so as to form a second emulsion 72 which has a small         average droplet size. Emulsions 68 and 72 are then combined in         module 56 to form the desired end emulsion. In this regard,         additional water 74 may advantageously be added to the system,         for example by adding to small droplet diameter emulsion 72, so         as to provide a final bimodal emulsion having a desired water         content, for example of greater than or equal to about 29%,         and/or further water can be added downstream of the emulsion         mixing process as well . . . .     -   . . . Turning now to FIG. 11, bimodal emulsions can         advantageously be formed by first making a plurality of         monomodal emulsions, and then mixing the emulsions in accordance         with the process described above. FIG. 11 shows two different         monomodal emulsions in terms of droplet size distributions, and         also shows the droplet size distribution for a bimodal or final         emulsion product prepared from the two monomodal emulsions. This         final product is stable and has desired properties.

The paragraphs above indicate the benefits from mixing multiple precursor emulsions; however, there is no instruction referencing how to get it done. This leaves the reader with the necessity to guess or experiment with mixing ratios, emulsion types, etc. In addition, there is no mention of the benefits of mixing emulsions.

The precursor emulsions may contain the same hydrocarbon material or different hydrocarbon materials depending upon the specific use of the emulsion. In addition, the particle size distributions and droplet size may be the same or different. In the instance where the size distributions are the same, the hydrocarbon material will be different in the discrete emulsions. As a further possibility, the composite emulsion may be a composite emulsion combined with a hydrocarbon in water emulsion. Similar to that noted above, the composite emulsion and hydrocarbon in water may comprise the same or different hydrocarbon material, same or different droplet size and/or the same or different particle size distribution.

According to a further aspect of one embodiment of the present invention there is provided a method of formulating a composite emulsion made from different hydrocarbon materials which possess widely differing viscosities and therefore widely differing emulsion preparation temperatures. Consequently, the precursor emulsion which is made at the lower temperature can be used as a cooling agent when mixed with the precursor emulsion which is made at the higher temperature. This obviates or reduces the need to use heat exchangers to reduce the temperature of emulsions which are made above 100 deg C. to below 100 deg C. prior to storage.

According to a further aspect of one embodiment of the present invention there is provided a method of formulating a composite emulsion having unimodal particle distribution with reduced viscosity relative to precursor emulsions used to form said composite emulsion: providing a system having an n-modal particle distribution; forming a precursor emulsion for each n-modal distribution present in the system, each precursor emulsion having a characteristic viscosity; and mixing precursor emulsions to form the composite emulsion with a unimodal size distribution and reduced viscosity relative to each precursor emulsion.

As briefly discussed herein previously, it has been found that by making use of the composite emulsion, the same has a viscosity which readily facilitates transportation, despite the high content of hydrocarbon material present in the emulsion. It is believed this is due to the unimodal particle size distribution which, inherently provides a broader spectrum of particle sizes. This, in turn, commensurately provides advantage in mixture viscosity.

A still further aspect of one embodiment of the present invention is to provide a method for transporting viscous hydrocarbon material comprising: providing a source of hydrocarbon material; generating a plurality of emulsions of the hydrocarbon material, each emulsion having a characteristic viscosity, each emulsion having a different particle size distribution; mixing the plurality of emulsions in a predetermined ratio to form a composite emulsion having a lower viscosity relative to the plurality of emulsions; and mobilizing the composite emulsion.

A still further aspect of one embodiment of the present invention is a method of maximizing viscous hydrocarbon content in an aqueous system for storage or transport, comprising: providing a hydrocarbon emulsion having a hydrocarbon internal phase volume sufficiently high such that the droplets in the emulsion are aspherical; converting the emulsion at least to a bimodal emulsion system; forming at least two precursor emulsions from the system; mixing the precursor emulsions in a predetermined ratio to effect reduced viscosity; and synthesizing a composite emulsion from the precursor emulsions having the reduced viscosity.

A still further aspect of one embodiment of the present invention is a method of formulating a composite emulsion having unimodal particle distribution with reduced viscosity relative to precursor emulsions: providing a system having an n-modal particle distribution; forming a precursor emulsion for each modal distribution present in the system; each the precursor emulsion having a characteristic viscosity; forming a plurality of composite emulsions each having a unimodal size distribution and reduced viscosity relative to each the precursor emulsions; and mixing the composite emulsions to form an amalgamated composite emulsion having a unimodal particle distribution and reduced viscosity relative to the viscosity of the composite emulsions.

In accordance with another beneficial aspect of one embodiment of the present invention, it was found that the HIPR (High Internal Phase Ratio) emulsions with extremely high hydrocarbon content could also be transported efficiently. By making use of the high internal phase ratio emulsion, it was discovered that these emulsions can be converted to at least a bimodal or n-modal emulsion system depending upon the number of particle size distributions within the HIPR emulsion and then these individual bimodal emulsions could be formed into precursor emulsions and mixed to form a composite emulsion in accordance with the methodology previously discussed herein. In this matter, aspherical or substantially non-spherical oil in water particles can be reconfigured or converted into discreet modes for individual emulsion synthesis with subsequent mixing for composition of a more favorably transportable composite emulsion. This has particular utility in permitting mobilization of high hydrocarbon content material without expensive unit operations conventionally attributed to processes in the prior art such as pre-heating, the addition of diluents or other viscosity reducing agents. The material can simply be converted, to a composite emulsion and once so converted, inherently has the same transportation advantages of the composite emulsions discussed herein previously.

A method of modifying at least one of the combustion, storage and transportation characteristics of an emulsion during at least one of pre-formation, at formation and post formation, comprising: providing an emulsion; treating the emulsion to a unit selected from the groups consisting of additive addition, mechanical processing, chemical processing, physical processing and combinations thereof; and modifying at least one characteristic of the characteristics of the emulsion from treatment.

After having discussed the limitations in the emulsion formulation art, the present invention in many of its aspects makes what, under present technology is extremely complex, very straight-forward with infinite range of design possibilities. In any given polydispersed system, there are a number of different particle sizes. Each one of these particle sizes could theoretically be mixed in any ratio to result in an infinite number of composite emulsions with varying polydispersity, droplet size and dynamic stability. It has been stated herein previously that prior art has attempted to teach methodology for preparation of a specific emulsion. Given the fact that any number of emulsions can be made with any number of precursor emulsions, as noted above, the task of predetermining the end result for the composite emulsion is a horrendous task which not only take significant experimental time with commensurate costs associated therewith, but becomes essentially impractical for the design chemist.

By the technology disclosed herein, dynamic stability of any emulsion can be improved, i.e., an existing composite emulsion. Further, the process allows for reconfiguration of an existing composite emulsion to improve or otherwise alter the physical and chemical properties. This is a marked advantage; it allows for essentially rendering a potentially ineffective emulsion effective for subsequent use. As will be appreciated, this is very beneficial for in situ or on-site fuel modification and obviates the need for power generation stations, etc. to have at their avail a number of different types of fuels. Once one set of parameters for a given fuel is achieved, the parameters can be altered to suit the burning requirements in a different environment.

Further, off-specification materials such as fuels, precursor materials for pharmaceutical and food production, etc. can be corrected to be acceptable or on the specification for subsequent use. This obviously presents sizable cost savings for material that would otherwise be discarded for lack of utility.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus generally described the invention, reference can now be made to the accompanying drawings illustrating preferred embodiments:

FIG. 1 shows the results obtained in Greenwood et al., and is a plot of viscosity measurements at varied small particle volume and total volume (from ref. Greenwood et al., [Colloids and Surfaces A: Physiochem. Eng. Aspects, 144 (1998) 139-147, Minimising the viscosity of concentrated dispersions by using bimodal particle size distributions]).

FIG. 2 is a plot of the effect of diameter ratio on suspension viscosity (Greenwood et al. [J. Colloid Interface Sci, 191, 11-21 (1997), The effect diameter ratio and volume ratio on the viscosity of bimodal suspensions of polymer lattices]).

FIGS. 3, 4 and 5 each indicate concentration and mixing ratio effects on suspension viscosity at diameter ratios of 6.37, 2.81 and 1.08.

FIG. 6 plots the composition (small particles by volume) on the relative viscosity of the bimodal suspension at a diameter ratio of 6.37. Total volume fractions are indicated to be 0.40, 0.45, 0.50, 0.55 and 0.60.

FIG. 7 plots the effect of the composition (small particles by volume) on the relative viscosity of the bimodal suspension at a diameter ratio of 2.81. Total volume fractions indicated are 0.40, 0.45, 0.50, 0.55 and 0.60.

FIG. 8 plots the composition (small particles by volume) on the relative viscosity of the bimodal suspension at a diameter ratio of 1.08. Total volume fractions indicated are 0.40, 0.45, 0.50, 0.55 and 0.60.

FIG. 9 plots viscosity as a function of total oil volume fractions.

FIG. 10 is a schematic illustration of the overall synthesis mechanism of the instant technology;

FIG. 10A is a schematic illustration of a variation in the overall synthesis mechanism of the instant technology;

FIG. 11 is a graphical illustration of particle size as a function of shear;

FIGS. 12A and 12B are graphical illustrations of viscosity as a function of droplet size ratio;

FIG. 13 is graphical illustration of percentage of oil in the emulsion as a function of further length;

FIG. 14 is a graphical illustration of two precursors and a composite emulsion of a surfactant in 70% NE Alberta bitumen for a median particle size of 5 μm and 24 μm;

FIG. 15 is a graphical illustration of the composite emulsion viscosity for varying percentages of the same median particle size;

FIG. 16 is a graphical illustration of a two modal distribution for North Eastern Alberta bitumen particles with two particle sizes (5 microns and 10 microns);

FIG. 17 is a graphical illustration of viscosity as a function of the percentage of 5 micron MSAR™ used in the precursory emulsion and percentage of 10 micron MSAR™ used in the second precursory emulsion;

FIGS. 18A through 18C illustrate particle distributions for composite emulsions formed from the 5 and 10 micron individual emulsions for 5 and 10 micron percentages of 20% and 80%, 50% and 50% and 80% and 20%, respectively;

FIG. 19 illustrates the individual distributions for a 6 micron 12 micron mode where both precursory emulsions are formed using a surfactant and a 70% content of refinery residue;

FIG. 20 illustrates a viscosity as a function of the MSAR™ mixture composed of 5 microns in the first emulsion and 12 microns in the second emulsion;

FIGS. 20A through 20C illustrate the result of the particle distribution in the composite emulsions for the 6 and 12 micron particles in the following percentages: 20% and 80%, 50% and 50% and 80% and 20%, respectively;

FIG. 21 is a graphical illustration of the precursors where emulsion number 1 comprises 6 micron median particle size distribution and emulsion to a 16 micron median particle size distribution;

FIG. 22 is a graphical representation of the viscosities of the MSAR™ mixtures composed of 6 micron and 16 micron 80/100 Asphalt MSAR™;

FIGS. 22A through 22C illustrate varying percentages of 6 micron and 16 micron particles, namely 20% and 80%, 80% and 20%, and 50% and 50%, respectively;

FIG. 23 is front view of a burner where the illustration is of a North Eastern Alberta bitumen MSAR™ fuel number 1 being combusted;

FIG. 24 is a side view of the flame illustrated in FIG. 23;

FIG. 25 is an illustration of the coke deposits on the nozzle subsequent to the combustion of the fuel being burned in FIGS. 23 and 24;

FIG. 26 is a view similar to FIG. 28 after a second burning run of MSAR™ fuel 1;

FIG. 27 is a view of the combustion from the burner of the North Eastern Alberta bitumen MSAR™ fuel 2;

FIG. 28 is a photograph of the nozzle after combustion of the MSAR™ fuel 2 illustrating the coke deposit;

FIG. 29 is a figure depicting the flame generated from the burning of the North Eastern Alberta bitumen MSAR™ composite fuel between the MSAR™ fuel 1 and MSAR™ fuel 2;

FIG. 30 is a side view of the flame of FIG. 29; and

FIG. 31 is an illustration of the burner nozzle illustrating the minimum deposition of coke on the nozzle.

It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 10, shown is the overall synthesis mechanism globally denoted by numeral 10. The synthesis mechanism includes two broad steps denoted by numerals 12 and 14. In step 12, a hydrocarbon material 16 is mixed with water 20 containing a surfactant 18 and the material, as a mixture, is mixed in a mixing device 22.

The hydrocarbon material may comprise any hydrocarbon material fuel, non limiting examples of which include natural gas, bitumen, fuel oil, heavy oil, residuum, emulsified fuel, multiphase superfine atomized residue (MSAR™), asphaltenes, petcoke, coal, and combinations thereof. It is desirable to employ hydrocarbon material of less than 18 API. The use of an emulsion stabilizer (a chemical composition which presents premature phase separation of the emulsion), stabilizes phase separation. The surfactants are useful for this as well as a host of other members in the class of stabilizers.

In terms of the surfactants, it is well known in this art that the surfactants may be non-ionic, zwitterionic, cationic or anionic or mixtures thereof. Further, they may be in a liquid, solid or gaseous state. It is well within the purview of the scope of this invention to use combinations of materials to achieve a properly dispersed system normally attributable to emulsions.

The mixer may comprise any suitable mixer known to those skilled in the art. Suitable amounts for the emulsion stabilizer or surfactant comprise between 0.01% by weight to 5.0% by weight of the emulsion with the hydrocarbon comprising any amount up to 90% by weight. In the example, a mixer such as a colloidal mill, is used. Once the materials are subjected to the colloidal mill a first precursor emulsion 24 is generated. Similar steps are effected to result in the second precursory emulsion 24′, with common steps from the preparation of emulsion one being denoted by similar numerals with prime designations.

Once precursor emulsion 24 and the second precursor emulsion 24′ are formed, the two are introduced into a mixing device 26 which may comprise a similar shear apparatus as the colloidal mill or more likely a further selected device such as an in-line static mixer.

In the individual emulsions 24 and 24′, one of the emulsions will have a smaller average particle diameter relative to the second emulsion. These are then mixed together in a predetermined ratio to form the composite emulsion 28 which is a polydispersed fuel emulsion. The predetermined ratio is determined by making use of a particle packing algorithm such as that which has been set forth in the discussion of the prior art. The final properties desired in the composite dictate the initial mix-in ratio. Thus, any emulsion can be formulated or designed with any composition of precursor emulsions. This is a very significant result; as has been discussed at length herein previously, previous attempts in this area of technology have not been able to provide for a “designer approach” to the formulation of emulsions. As discussed previously, in situations where certain parameters or properties were desired in the final composite emulsion, a substantial amount of experimentation and conjecture was required. This obviously requires a significant amount of time with potentially undesirable results. With the instant technology, the result is easily achieved. The final parameters for the composite are determined and these are inputted into the algorithm which then analyses the best possible result in terms of polydispersity, viscosity and maximum packing fraction for ideal results for the final composite. It will be glaringly apparent that this is ubiquitously employable in all areas of technology. One of the more favourable areas of applicability is, as discussed, in a high-temperature furnace for use in, for example, steam generators. Depending upon the configuration of the plant, differently sized furnaces are sometimes required even within the same plant. This poses a great deal of difficulty for the engineer, since a number of different fuels are then required to optimize burn, depending upon the length of the furnace, among other properties. It is clearly disadvantageous to be required to store or otherwise retain several different fuels when one formulation which can be modified on site.

Returning to the algorithm, it is known that this computer model was previously applied to solid based rocket fuels and by making use of the algorithm in the synthesis of a composite emulsion, a very successful result has been encountered. One of the particularly attractive results is that the composite emulsion has a viscosity that is less than the viscosity of the precursor emulsions by a factor of between 3 and 5 times the viscosity of the precursor emulsion containing the small droplets. A further advantage that flows from this unification of unrelated technologies is the requirement for lower preheat temperatures in the composite emulsion as opposed to those preheat temperatures required for the previous or precursor emulsions.

Conveniently, the composite emulsion also has been found to have much improved dynamic and static stability and handling (anything in-between manufacture and burner tip, e.g. storage, valves, pipes, tanks, etc.) characteristics and therefore easier storage and transportation possibilities. In burn testing, the composite emulsions provided greater than 99.9% carbon burnout, despite the fact that the emulsion contained a high percentage of the hydrocarbon material in water.

Referring now to FIG. 10A, shown is a variation of the overall arrangement shown in FIG. 10. In this embodiment, the process may be modified at various stages to effect the transportation storage and/or combustion of the individual components within the emulsions or the composite emulsion itself. In this manner, FIG. 10A provides for modification of at least one of the above noted aspects by modification at the pre-synthesis mixing point prior to the surfactant and water entering the mill 22 as denoted by numeral 30 or as a further option by modifying the hydrocarbon prior to introduction to the mill, this step being indicated by numeral 32. As a further possibility, the emulsion may be modified at the point of fabrication, denoted by numeral 34 or subsequent to formation at 36. In respect of similar numerals with prime designations, these steps apply to emulsion number 2 designated by numeral 24′. As a further possibility, once the first emulsion 24 and second emulsion 24′ are introduced, they may modified at mixer 26 denoted by numeral 38 or subsequently modified once the composite emulsion 28 has been formed. This step is denoted by numeral 40.

By the variation in this process as depicted by FIG. 10A, the emulsion may be modified in terms of combustion, storage and/or transportation characteristics during at least one of pre-formation, at formation and post formation where the modification involves a unit operation selected from at least additive addition, mechanical processing, chemical processing and physical processing, as well as combinations thereof. The additive addition will be discussed herein after.

Referring now to FIG. 11, shown is a schematic graphical illustration of particle size as a function of the amount of shear. This permits the selection of different particle size distributions for the emulsions by changing the amount of shear used to make particles for the emulsion. It is known that the amount of shear is related to the average particle size and width of distribution as shown in FIG. 11. The lowest droplet size is related to the parameters used to formulate the emulsion. The shear amount is increased by increasing the residence time in the mixing device, or increasing the speed at which the rotatable mixing device rotates.

It has been found that it is convenient to maintain the surfactant concentration relative to the oil content as substantively the same for precursor emulsions for purposes of stability. This is exemplary only, variations in the concentration of the surfactant can occur depending upon the final desired characteristics for the composite emulsion. In situations when different surfactants are used for different composite emulsions, the surfactants will, for course, be compatible. The examples have been discussed previously and other examples will be apparent to those skilled.

Referring now to FIGS. 12A and 12B, shown are schematic graphical illustrations of viscosity as a function of a ratio of small droplets versus big droplets with the larger droplets being represented on the left hand side of the graphs.

Referring now to FIG. 13, the oil content in the emulsion as a function of the length of furnace required to completely burn the fuel.

Referring now to FIG. 14, shown is pre-mix particle distributions for a bimodal system where numeral 1 represents an emulsion containing surfactant with 70% North Eastern Alberta bitumen with the balance comprising water. The first distribution was formulated using a high shear mixer at a high revolution. The median particle size in this distribution was 5 microns whereas in distribution number 2, the median particle size was 24 microns. In the premix it is evident that each emulsion possesses a distinctly different mean and median droplet size.

FIG. 15 plots the composition (small particles by volume) on the relative viscosity of the bimodal suspension at a diameter ratio of 6.37. Total volume fractions indicated are 0.40, 0.45, 0.50, 0.55 and 0.60.

FIG. 15 is a graphical representation of viscosity as a function of percentage of 5 micron MSAR™ emulsion and 24 micron MSAR™ used in the mixture. Inset FIG. 15A is a distribution representation for a 20% 5 micron and 80% 24 micron mixture having a characteristic viscosity indicated by the arrow in the graph of FIG. 15, whereas FIG. 15B is an inset where the mixture or composite emulsion contained 80% 5 micron particle size and 20% 24 micron particle size with the arrow pointing in FIG. 15 to the characteristic viscosity. Finally, inset FIG. 15C depicts a 50/50 blend of 24 micron and 5 micron particles with the characteristic of viscosity being indicated by the arrow. From a review of FIGS. 15A through 15C, it is evident that the particle distribution representations are effectively unimodal despite containing two individual emulsions which independently possess distinctly different mean and median droplet sizes.

Referring now to FIG. 15D, shown is a ternary diagram for a three-fraction system of 1 micron particles, 5 micron particles and 10 micron particles. As is generally known, these plots are effective to display packing fractions. The data can be interpreted to determine what combinations of the particles would yield the best possible packing fraction. In the ternary diagram illustrated, the data is representative of 67 different particle mix combinations. The varying shading illustrates different packing fractions with the range comprising 0.62 through 0.76. As is evident from the Figure, in order to determine the best possible packing fraction, the use of an algorithm in this scenario is critical to avoid the guesswork involved in determining the best packing fraction. It will be appreciated by those skilled in the art that it would be next to impossible to try to predict what is depicted in FIG. 6D. Even with the packing fractions indicated, there is a significant amount of variation in the particle fraction percentage between, for example, the 0.74 and 0.76 range. Accordingly, the use of the algorithm not only expedites compositional details for the best packing fraction, but also can be used by the designer to select different combinations within an area of the diagram common to a certain packing fraction.

As a further representation, FIG. 16 provides a North Eastern Alberta bitumen particle distribution where there is a greater degree of overlap between the two modal distributions in view of the median particle size. In this representation, similar materials were used with respect to the previous discussion with the 5 micron median particle distribution being represented by numeral 1 which occurred at a relatively high speed, whereas peak 2 comprises medial particle distribution of 10 microns which was created at a lower speed. This is an example; mixing can occur in a low and high intensity mixer with the rpm selected based on final requirements.

FIG. 17 illustrates a viscosity as a function of the percentage of 5 micron MSAR™ used in the precursory emulsion and percentage of 10 micron MSAR™ used in the second precursory emulsion. Insets 18A, 18B, and 18C illustrate particle distributions for composite emulsion formed from the 5 and 10 micron individual emulsions for 5 and 10 micron percentages of 20% and 80%, 50% and 50%, and 80% and 20%, respectively. Individual arrows from each of insets 18A through 18C are representative of the viscosity of the individual final composite mixtures of insets 18A, 18B and 18C.

In FIG. 19, a further hydrocarbon material was employed for synthesizing the composite emulsion. FIG. 19 illustrates the individual distributions for a 6 micron and 12 micron mode where both precursor emulsions were formed using a suitable surfactant and a 70% content of refinery tank 9 with a balance of water. The contents of the refinery residue are approximately 10% gas oil and 90% viscous hydrocarbon material. The 6 micron distribution was generated at a relatively high speed, whereas the 12 micron was generated at a lower speed.

FIG. 20 illustrates the viscosity as a function of the MSAR™ mixture composed of 5 microns in the first emulsion and 12 microns in the second emulsion. FIGS. 20A through 20C illustrate the results of the particle distribution in the composite emulsion for the 6 and 12 micron particles in the following percentages: 20% and 80%, 50% and 50% and 80% and 20%, respectively.

As is evident from the inset illustrations, each has a characteristic viscosity indicated on the graphical representation of FIG. 20. Further, similar to the previous examples noted, the composite emulsion in all cases is effectively unimodal and accordingly provides a broad particle size distribution.

FIG. 21 tabulates the characteristics of pre-cursor emulsion where emulsion number 1 comprises 6 micron median particle size distribution and emulsion 2 a 16 micron median particle size distribution. In this example, the surfactant was employed as the surfactant with the hydrocarbon material comprising 70% 80/100 Asphalt with the balance being water. The 6 micron distribution was formulated using the mill at a relatively high speed where the 16 micron was synthesized at a lower speed.

Similar data to the examples presented previously are presented in FIG. 22 where the viscosity is represented. Inset FIGS. 22A through 22C represent specific composite emulsion formulations of 6 and 16 micron distributions in the following amounts: 20% and 80%, 80% and 20%, and 50% and 50%, respectively.

Once again, the composite emulsion demonstrates a unimodal particle distribution with characteristic viscosities for each of the insets 22A through 22C.

From the results, it is evident that the instant methodology results in the desirable formulation of unimodal composite fuel emulsion from discrete precursory emulsions. It is known that the oil content or hydrocarbon material content of oil in water emulsions of the prior art is generally limited to approximately 70% since greater content beyond this point increases the viscosity of the emulsion exponentially. This is clearly contrary to the desired properties that have been achieved with the instant methodology. By making use of the protocol as set forth herein, the oil content can be increased to up to 90% whilst still maintaining relatively low viscosities compared with conventional or HIPR emulsification. It is believed that the packing of the droplets in the multiple polydispersed fuel emulsions set forth herein is significantly better in normal emulsions not presenting unimodal distributions.

A host of very useful features flow from the use of this methodology not only to make an improved emulsified fuel with higher carbon burnout than the individual emulsions in the composite, but also the lower water requirement for transportation.

As discussed briefly, one of the major advantages of the instant technology is that HIPR emulsions which are characteristically composed of aspherical particles which are generally polyhedral which can be converted into individual emulsions and then subsequently combined to form a composite mixture having the advantages that flow from the instant technology. In this manner, the HIPR emulsions can be converted to provide the desirable properties of a composite emulsion in terms of having a wider particle distribution with reduced viscosity and improved combustion. It is a well known fact that HIPR emulsions have exceptionally high viscosities, and are very shear thinning. It has not been previously proposed to convert HIPR emulsions into discrete emulsions for a combination such as that which is disclosed herein to provide for reduced viscosity with enhanced combustion. It has not been previously recognized to employ HIPR emulsions which are capable of having a 99.9% carbon burnout rate.

With respect to convenience of use, the emulsion technology set forth herein allows the emulsion to be designed for the furnace or burning arrangement individually as opposed to having to design a furnace to specifically burn the emulsion. The cost savings on this point are extremely substantial; the modification of the emulsion is obviously a much less involved exercise than having to design and fabricate a new piece of expensive equipment.

Further, depending upon economics and the requirements for the composite emulsion the precursor emulsions are not limited in number and are well within the scope of the instant technology to provide an n-modal system. The individual emulsions would have to be formulated and then subsequently mixed together to form the composite emulsion as an attendant feature to this aspect of the invention, individual groups of emulsions may be mixed to form composite emulsions and the so formed composite emulsions then further mixed to form an amalgamated emulsion of individual composite emulsions. In terms of bi or multi-modal distributions used to form a composite emulsion, the composite may be reintroduced into a shear or mixing device to form a processed composite emulsion.

Having now delineated the details of the invention, reference will now be made to the following example:

Example

Three fuel types were examined:

-   -   1) North Eastern Alberta bitumen MSAR™ fuel 2 with particle size         5.5 μm;     -   2) North Eastern Alberta bitumen MSAR™ fuel 1 with particle size         22 μm; and     -   3) 50/50 mixture of North Eastern Alberta bitumen MSAR™ fuel 1         and MSAR™ fuel 2 with particle size 5-22 μm.

Experiments began with the fuel having the larger droplet (MSAR™ fuel 2).

A fuel firing rate of 30 kg/h, lower than the normal 36 kg/h, was used to avoid possible fuel plugging since the fuel contained larger sized droplets. The same fuel firing rate was used for the other fuel types to maintain consistency among the conditions.

The initial temperature for the MSAR™ fuel 1 was a fuel temperature of 85° C. and was slowly increased to 100° C., based on the flame characteristics observed.

Other parameters followed for the protocol were:

Atomizing air temperature of 108° C.;

-   -   78-79° C. at burner;     -   Combustion air temperature of 108° C.     -   O₂ 0.6.7, 6.2

Parameters observed for the MSAR™ fuel 2 fuel type were:

An atomizing air temperature of 84° C.;

-   -   Combustion air temperature of 84° C.;     -   A fuel temperature of 65° C.; and     -   O₂ 5.2, 5.3

In terms of the data for this methodology, the terms used in the tables have the following meanings/explanations:

-   -   Fuel: is the input to the furnace (mass rate, temperature and         pressure are the same for each of the three cases, i.e., 22         microns, 5 microns and composite)     -   Atomizing air: is the air that is used for the primary         atomization of the liquid droplet. Typically, primary         atomization usually produces a liquid droplet of 50 to 200         microns.     -   Combustion air: is the major source of oxygen for the         combustion.     -   Flue gas: the emissions are normalized to 3.5% oxygen content in         the flue gas. For this reason, two columns are employed; one for         fuel, which is measured, and one which is normalized.     -   Carbon monoxide emissions: the amount of carbon monoxide is an         indication of incomplete combustion.     -   Particulates: the amount of carbon on the particulates is an         indication of incomplete combustion. The more carbon on the         particulates, the greater the degree of incomplete combustion.     -   Thermal transfer rate: this is a measure of the key transfer         rate measured radially to the flame. All of the emulsions show         higher radial heat transfer rate than natural gas. The heat         transfer rate of all three emulsions are somewhat the same in         each instance.

TABLE 2 Properties of MSAR Fuels (wet basis) 22 μm 5 μm 50:50 Mixture MSAR MSAR (22 and 5 μm) Density by Helium 1005 1004 1006 Pyrometer at 15° C., kg/m³ Calorific Value, cal/g 6745 7003 6860 MJ/kg 28.24 29.32 28.72 BTU/lb 12141 12605 12348 Water by distillation, 30 30 30 wt % Carbon, wt % 55.4 59.2 58.5 Hydrogen, wt % 11.5 11.0 10.5 Sulphur, wt % 3.29 3.41 3.45 Nitrogen, wt % <0.50 <0.50 <0.50 Ash, wt % 0.051 0.034 0.049

TABLE 3 Furnace Operating Conditions and Emission Results Natural 22 μm 5 μm 50:50 Mixture Gas MSAR MSAR (22 and μm) Fuel Flow rate, kg/h 20 29.69 29.80 29.83 Thermal input GJ/h 1.063 0.839 0.874 0.857 MMBTU/h 1.007 0.795 0.828 0.812 KW 295 233 243 239 Temperature, ° C. At tank outlet — 52.8 53.0 52.8 At burner 29.5 78.4 75.3 76.5 Pressure at burner, kPa — 96 103 96 Mean particle size μm — 22 5 22 &5 Atomizing air Flow rate, kg/h at NTP 39 29 29 25 Temperature at burner, 23 97 84 80 ° C. Pressure at burner, kPa 69 21 28 14 Combustion air Flow rate, kg/h at NTP 382 424 433 468 Temperature at burner, 33 107 83 88 ° C. Flue gas Furnace exit 406 393 404 431 temperature, ° C. Flow rate, Nm³/MJ 0.256 0.364 0.332 0.321 of fuel * Particulate — 0.189 0.124 0.146 loading, g/Nm³ Flue gas analyses, volume basis O₂, % 3.5 3.5 3.5 3.5 5.79 5.2 4.4 CO₂, % 9.1 12.9 13.0 12.9 11.20 11.7 12.2 CO, ppm 13 90 71 46 78 60 44 NO, ppm 64 231 344 300 201 290 284 SO₂, ppm — 2794 2853 2752 2426 2581 2603 Flue gas emission, g/MJ of fuel NO_(x) 0.022 0.098 0.129 0.122 SO₂ — 2.526 2.452 2.392 Particulate — 0.069 0.042 0.047 Carbon on particulate, — 39.2/38.5 33.0/3.4 6.1/2.3 wt % ** Particulate concentra- — 0.0028 0.0018 0.0019 tion, g/g of fuel * Calculations based on stoichiometric combustion and oxygen content of flue gas ** The carbon result is an estimate only as filter paper was analyzed along with the powder sample

TABLE 4 Comparison of Thermal Heat Transfer for Natural Gas and MSAR Natural 22 μm 5 μm 50:50 Mixture Gas MSAR MSAR 22 and μm) Fuel Thermal input, GJ/h 1.063 0.839 0.874 0.857 MMBTU/h 1.007 0.795 0.828 0.812 KW 295 233 243 239 Thermal heat transfer, kW Circuit 1-10 123.95 116.21 117.38 117.13 Circuit 11-20 23.11 32.45 27.84 33.05 Circuit 21-28 1.85 1.62 0.97 1.16 Total (1-28) 157.91 150.28 146.19 151.94 Total W/cm² of 1.21 1.16 1.12 1.17 thermal surface Heat transfer rate, 0.149 0.208 0.175 0.171 kW/MJ of fuel input Percent of thermal 53.5 64.4 60.1 63.6 fuel input extracted in thermal plate

From a review of the data presented in the tables and, with specific reference to Table 4 it is evident that the MSAR™ blend or the composite emulsion provides a high thermal efficiency which exceeds the value for the 5 μm MSAR™ and approximates the 22 μm MSAR™.

In furtherance of the significant benefits that have been realized in the composite emulsion, Table 3 provides flue gas emission data which again provides evidence that the NO_(x) and SO₂ emissions are very appealing from an environmental point of view in the blend. It is particularly note worthy that the MSAR™ blend composite has a lower carbon content in the particulates and a lower CO concentration in the flue gas than the precursor emulsions, indicating a much better carbon burnout for the composite emulsion.

Perhaps the most appealing group of data is provided for in Table 4 where the thermal heat transfer data is indicated. Reference to the percent of thermal fuel input extracted in the examples clearly provides for very favourable energy for the composite relative to that for natural gas.

The data presented herein is further corroborated by FIGS. 22 through 30.

Referring to FIG. 22, shown is a photograph of a burner where the North Eastern Alberta bitumen MSAR™ fuel 1 is being combusted. The flame shape is illustrated in the Figure.

FIG. 23 illustrates a side view of the flame from the burner of the fuel being burned in FIG. 22.

FIGS. 24 and 25 illustrate the coke deposit on the nozzle of the burner after the first run of burn, while FIG. 25 illustrates the coke deposit on the nozzle of the burner after a second run; the difference being fairly significant.

FIG. 26 provides a view of the burner during the burn of the North Eastern Alberta bitumen MSAR™ fuel 2.

FIG. 27 illustrates the coke deposit on the nozzle of the burner subsequent to the combustion of the MSAR™ fuel 2.

In FIG. 28, the burning of the composite emulsion is indicated in the photograph. It is interesting to note that the flame shape is much more consolidated than the flame shape of the individual precursor emulsions when burned. This is further corroborated by FIG. 29, which shows a fairly significant flame length and intensity when taken from a side view of the burner. As discussed herein previously with respect to the burn characteristics and other features of the composite emulsion, FIG. 30 illustrates the cleanliness of the flame; the coke deposit on the nozzle subsequent to burning is virtually non-existent when one compares this illustration with the coke deposits from FIG. 25 relating to the combustion of MSAR™ fuel 1.

CONCLUSIONS

Having regard to the photographic data and physical data presented during the testing of the composite emulsion, it is evident that the composite emulsion has many significant benefits over the burning of the precursor emulsions and in many cases approximates the beneficial features of burning natural gas. Obviously, the combustion of the composite emulsion provides a more desirable energy output from a lower monoxide emission, lower coke deposits at the burner nozzle, lower sulfur dioxide emissions among other very desirable properties. As evinced form the Figures, the composite emulsion flame characteristics provide for a much brighter and more stable flame with less brownish discolouration, lower carbon monoxide emission among other features. 

1. An emulsion, comprising a composite of a plurality of hydrocarbon in water emulsions and emulsion stabilizer, said composite having a unimodal particle distribution with a single mode absent local maxima, said hydrocarbon being present in an amount of between 64% and 90% by volume.
 2. The emulsion as set forth in claim 1, wherein said composite comprises at least two different precursor emulsions.
 3. The emulsion as set forth in claim 2, wherein said precursor emulsions each contain a different hydrocarbon particle size.
 4. The emulsion as set forth in claim 3, wherein said precursor emulsions contain the same hydrocarbon material.
 5. The emulsion as set forth in claim 3, wherein said precursor emulsions contain different hydrocarbon material.
 6. The emulsion as set forth in claim 3, wherein each precursor emulsion has a different rate of combustion.
 7. The emulsion as set forth in claim 5, wherein said composite is a composite containing at least two different emulsions in a predetermined ratio.
 8. The emulsion as set forth in claim 3, wherein said particle size of one emulsion is large relative to said particle size a second emulsion.
 9. The emulsion as set forth in claim 7, wherein each precursor emulsion has a characteristic viscosity, said composite emulsion fuel having a viscosity which is less than each characteristic viscosity of each precursor emulsion.
 10. The emulsion as set forth in claim 9, wherein said composite emulsion has a viscosity between 300% and 500% less than the viscosity of the emulsion containing smaller particles.
 11. The emulsion as set forth in claim 1, wherein said composite emulsion has a carbon burnout rate of at least 99.9%.
 12. The emulsion as set forth in claim 1, wherein paid composite has said unimodal particle size distribution formed from mixing a bimodal distribution of said at least two precursor emulsions.
 13. The emulsion as set forth in claim 1, wherein said composite is a multiple emulsion polydispersed fuel.
 14. The emulsion as set forth in claim 1, wherein said fuel is a liquid fuel emulsified in an aqueous matrix hydrocarbon.
 15. The emulsion as set forth in claim 1, wherein said hydrocarbon material comprises less than 18 API.
 16. The emulsion as set forth in claim 1, wherein said emulsion stabilizer is present in an amount between 0.01% and 5.0% by weight of the composite emulsion.
 17. The emulsion as set forth in claim 16, wherein said emulsion stabilizer is a surfactant.
 18. A method of formulating/a composite emulsion having unimodal particle size distribution with reduced viscosity relative to precursor emulsions used to form said composite emulsion, comprising: providing a system having an n-modal particle distribution mixture; forming a precursor emulsion for each n-modal distribution present in said mixture, each precursor emulsion having a characteristic viscosity; and mixing precursor emulsions in a predetermined ratio as determined by desired characteristics of the composite emulsion to form said composite emulsion with said unimodal particle size distribution, reduced viscosity relative to each said precursor emulsion and said desired characteristics, wherein said unimodal particle distribution has a single mode absent local maxima.
 19. The method as set forth in claim 18, wherein said mixing comprises a shear mixing device.
 20. The method as set forth in claim 18, wherein said mixture is a composite emulsion formed from at least two precursor emulsions.
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